Optimum pH and pH Stability of Crude Polyphenol Oxidase (PPO) Extracted from Five Fruit Samples Commonly Consumed in Kano State, Nigeria

Abstract

The effect of pH on the activity and stability of crude polyphenol oxidase (PPO) extracted from garden egg (Solanum aethiopicum), pawpaw (Carica papaya), pumpkin (Cucurbita pepo), guava (Psidium guajava) and bush mango (Irvingia gabonnensis) fruits were studied. Catechol at concentration of 20 mM was used as a substrate while sodium acetate buffer (0.2 M), pH range between 3.0– 5.5 and sodium phosphate buffer(0.2 M) , pH range between 6.0– 8.5 were used to determine the effect of pH on the PPO activity. Optimum pH values were found to be 6.0,6.5,6.0, 4.5 and 4.0/or 8.0 for the enzyme extracted from Solanum aethiopicum, Carica papaya, Cucurbita pepo, Psidium guajava and Irvingia gabonnensis respectively. The enzyme was found to be stable at the pH range of 5.0-7.5 for the enzyme extracted from garden egg, 6.0-8.0 for that from pawpaw, 4.5-7.0 for that from pumpkin, 4.0-6.5 for that from guava and 3.5-5.5 and 7.0-8.0 for that from bush mango respectively. Increase or decrease of pH from the ranges would cause decrease in the activity of the enzyme, and can be a good way of controlling undesirable changes caused by it in foods.

Keywords: Optimum pH, pH stability, Polyphenol oxidase, Common fruits.